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Question 30: NCERT Solutions for 12th Class Physics: Chapter 11-Dual Nature of Radiation and Matter

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Question 30: NCERT Solutions for 12th Class Physics: Chapter 11-Dual Nature of Radiation and Matter

Light of intensity 10-5 W m-2 falls on a sodium photo-cell of surface area 2 cm2. Assuming that the top 5 layers of sodium absorb the incident energy, estimate time required for photoelectric emission in the wave-picture of radiation. The work function for the metal is given to be about 2 eV. What is the implication of your answer?

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  1. Solution:
    Wave picture of radiation state that incident energy is uniformly distributed among all the electrons continuously. Let us first calculate the total number of recipient electrons in-5 layers of sodium. Consider each sodium atom has one electron free as conduction electron. Effective atomic area = 10-20 m2 Number of conduction electrons in 5 layers

    Where experimental observation shows that emission of photo electrons is instantaneous = 10-9 sec Thus wave picture fails to explain photoelectric effect.

    Check the complete chapter with solutions.
    NCERT Solutions for 12th Class Physics: Chapter 11-Dual Nature of Radiation and Matter